A few things to measure "strength"
For one it depends on the application or program. Say you're playing a game. Most likely it's only going to utilize a single maybe two cores. So i guess in that sense "Strength" is entirely relative.
Where as if you had a 4 core cpu and were rendering a video with hyperthreading you'd have a Faster rendering time. So in that sense, A 4 core for that application is "stronger"
At the same time the speed or gigahertz would be a kind of 1:1 ratio. Say you had a 4 core cpu that had a core clock at 4ghz when rendering video's it would be faster then a 3.0ghz clocked 4 core.
The same for gaming, if you had a 4 core cpu vs a 2 core in a game optimized for a 2 core cpu. And the 4 core had a clock of 3.5ghz and the 2 core had a clock of 4.5ghz.
Because that program or application is optimized for only using the minimal amount of cores, the 2 core would be better in that specific situation.
That isn't to say all games follow that rule newer games actually do better with 4 cores and hyperthreading resulting in slightly higher fps, and for the most part stability in frames. Say you go from outside a building to the inside. On a 2 core you'd have a much more significant drop in frames then a 4 core, so i guess you can factor that into immersion.
But gighertz aren't everything either , say you were working in an enterprise environment. And you worked that hold sensitive data an entire company would need to access, quickly. Well then you'd need a cpu with a lot of cores say 18. But the clock speed would have to be around 2.00-2.4 ghz. Because the heat built by those kinds of cpu's for one would make it impractical to have high temps and for 2 in those kinds of environments or situations you'd need more cores for better data management.
Another example would be. If you had a 4 core cpu with 8 hyperthreads at a 4.5ghz overclock. From the early 2000's.
And say you see a new cpu which had 4 cores and 8 hyperthreads at 3.5ghz base clock. Which cpu would be better. Well it depends again. In a pure performance test sure the 4.5ghz is more. But more then not the 3.5ghz one that just released. As it would have updated instruction sets and updated micro architecture leading to better more efficient usage in programs.
Then theirs intel and amd. For the most part i'd lean more towards intel. If you plan on using the specific features that intel offers. If not, then go with amd. Their both perfectly fine cards. It depends on what you use them for
So long story short. It depends, what are you going to use the cpu for. Theirs no real "strong" cpu.